Sewage system



NOV. 22, 1938. R 5 RANKlN 2,137,966

SEWAGE SYSTEM Filed March 12, 1935 4 Sheets-Sheet l ATTORNEY.

R. S. RANKIN SEWAGE SYSTEM Nov; 22, 1938.

Filed March 12, 1955 4 Sheets-Sheet 2 FIG.9.

INVENTOR. RENVILLE S. RANKIN ATTORNEY.

Nqv. 22, 1938. I R. s. RANKIN SEWAGE SYSTEM Filed March 12,, 1935 4Sheets-Sheet 3 INVENTOR.

RENVILLE S. RANKIN ATTORNEY.

Nov. 22, 1938. R. s. RANKIN 2,137,966

SEWAGE SYSTEM Filed March 12, 1935 4 Sheets-Sheet 4 FIG.7.

INVENTOR.

RENVILLE s. RANKIN ATTORNEY.

Patented Nov. 22, 1938 PATENT OFFICE SEWAGE SYSTEM Renvllle S. Rankin,Chicago, 111., assignor to The Dorr Company, Inc., New York, N. Y., acorporation of Delaware Application March 12,

14 Claims.

This invention relates to a clarification and treatment system for theremoval of suspended solids from liquids. More particularly it relatesto improvements in the operation and arrangement of the system withregard to potential operating changes in response to certain varyingdemands.

With regard to its field of application this invention relatespreferably, although not exclusively, to sewage treatment, or morespecifically to improvements in a clarifying system for sewage treatmentin which periodic operating changes are desired in view of certainrequirements .of flexibility, economy,and other plant operatingprinciples, and also in view of such demands as made upon the sewageplant according to seasonal conditions and fluctuations.

To understand a difficulty in the case of sewage clarification,according to one aspect a problem exists in the layout of sewage plants,which has to do with the fact that, as a rule, there is a scantiness ofhydraulic head between the point of raw sewage supply and the lowestpossible clarifier overflow elevation, so that a desired grav ity flowto and from the clarifiers can often only be obtained by a very closemargin. In a tentative example the. upper limitation of the headavailable may be determined by a long approach from the respectivemunicipality which the sew- 9 age plant serves, while the lower limitmight be controlled by the respective water levels of a stream or bodyof water into which the clarifier overflow is to discharge.

Consequently, in this respect this invention 5 contemplates having abattery of clarifiers changeable from parallel to series operation.Parallel operation can be satisfied with a smaller margin of head withboth clarifiers arranged on or for operating at substantially the samelevel. Series operation of the clarifiers requires additional head tocompensate for the necessary drop between the primary and secondaryclarifiers.

Another reason to account for the preference underlying this inventionof having the clarifiers in the sewage plant arrangeable for paralleland for series operation respectively, lies in a requirement fo'rchemically dosing the sewage preferably at certain points of theflowsheet. Such dosing may comprise the addition of a chemicalprecipitating agent at certain seasons of the year.

That is to say, when'dosing is required,- as for instance during thesummer months, it is preferred to interpose such dosing step between aprimary and a secondary clarifier, therefore sea ries operation of theclarifiers is desired atsuch 1935, Serial No. 10,660

time. This specific method of'dosing is advocated because it iseconomical in the use of coagulating or precipitating agents and ispreferable in certain instances to the dosing of the raw sewage at apoint ahead of the clarifiers. During 5 the winter months and otherwisehowever it may be desirable to omit the dosing step, and substituteoperation of the clarifiers in parallel instead of series.

Also certain requirements with regard to the 10 subsequent treatment bydigestion of the respective clarifier sludges have a bearing upon thepreference of dosing between clarifier stages, inasmuch as this makes asubstantial percentage of undosed clarifier sludge available forsubsequcnt digestion.

Objects of the invention are to produce a clarification plant, orclarification section of a plant, or sewage treatinent plant, which isflexible in operation, which is economical in dosing and powerrequirements and in total operating efliciency, which is optionallyoperable in parallel and series respectively preferably at a minimumtotal of hydraulic head, and which altogether is simple to operate inview of changing operating requirements. To this end the inventioncontemplates the arrangement of a pair of clarifiers at substantiallyequal overflow levels and thus adapted for parallel operation, incombination with pressure boosting means operative to make up for thehead loss when switching the clarifiers from parallel to series, andpreferably v inoperative when returning to parallel'operation. Onefeature therefore proposes an arrangement v according to which a liquidsupply channel has interposed in a portion thereof a rotary mixingdevice of the type which has suiilcient centrifugal efiect to act as alow lift pump.

This feature can therefore be said to reside in the selective use of acombined mixing device and low lift pump in a fiow sheet which isalternately operable with clarifiers parallel or in series.

Other features relate to a system of interconnections between therespective operating points of the clarification or treatment plant forselectively effecting a desired variety of operating changes. U

Other features revolve around.the details of structural arrangement andoperation of 'a liquid conditioning and flocculating unit to be usedcific arrangement of a low pressure pumping means for boosting gravityflow in a liquid clarification system, or to the use for this purpose ofwhat is known and may be referred to as a turbomixer or turboflash-mixer".

A preferrecl embodiment therefore in a sewage treatment plant, whilesimple, compact, and otherwise capable of meeting the various primerequirements set forth above, permits variant modes of operation; withselective use of the clarifiers, flocculating devices, mixing chamber,mixing device, and various auxiliary channels.

That is to say, with parallel connection of the clariflers theclarification plant isselectively operable: with or without dosing inthe mixing device, or with or without a flocculating step following themixing step.

The advantages derived from the foregoing volves the mixing of rawprimary sludge with.

chemically precipitated secondary sludge, which for the purpose ofdigestion is; considered preferable to digesting sludge which has beenwholly precipitated chemically.

The invention possesses other objects and features of advantage, some ofwhich with the foregoing will be set forth in the following description.In the following description and in the claims, parts will be identifiedby specific names for convenience, but they are intended to be asgeneric in their application to similar parts as the art will permit. Inthe accompanying drawings there has been illustrated the best embodimentof the invention known to me, but such embodiment is to be regarded astypical only 0. many possible embodiments, and the invention is not tobe limited thereto.

In particular there are possible within the scope of this invention avariety of operating combinations not enumerated above, such varietybeing covered by the appended description, claims, and drawings.

The novel features that I consider charactera derstood from thefollowing description of a specific embodiment when read in connectionwith the accompanying drawings in which:

Fig. 1 is a diagram showing parallel operation of the clarifiers, withconnections active to bypass the fiocculating unit.

Fig. 2 is a diagram showing series operation of the clarifiers, withconnections active to by-pass the flocculating unit.

Fig. 3 is a diagram showing parallel operation of the clarifiers, withconnections arranged to include the fiocculator unit.

Fig. 4 is a diagram showing series operation of the clarifiers, andconnections arranged to include the flocculating unit intermediate theclarifier's.

Fig. 5 is a diagram showing the clariflers in series with onefiocculator section ahead of the first clarifier, and the otherflocculating section intermediate the clarifiers.

Fig. 6 is an enlarged plan view of the conditioning and flocculatingunit including premixing and distributing chambers.

Fig. '7 is a longitudinal section of the conditioning and flocculatingunit, taken upon Fig. 6.

Fig. 8 is an enlarged detail section of the combined mixing and lowpressure pumping device. Fig. 9 is an end view upon the flocculatingtank and the clarifler tanks associated therewith.

Figures 1 to 5 show flowsheets disclosing diagrammatically a variety ofoperating connec- .tions which may be selectively established in apreferred clarification or .treatment system according to thisinvention. The system includes as operating elements: A pair ofmechanically cleaned clarifiers III and H; a liquid conditioning andflocculating unit collectively indicated by the numeral I2, andcomprising a pair of individual flocculating sections or units I3 and H;a

. conditioning or mixing chamber or unit l5 associated with the influentend of the flocculating units; a receiving chamber i6 for the mixingchamber; and a control chamber or arrangement I I equipped for selectivefeed distribution to various sections of the system.

The numeral l3 indicates an auxiliary arrangement for dispensing acoagulating or precipitating agent or chemical; "la a feed line thereforjointly comprising a device for causing coagulating precipitable solidsin the liquid. At l9 and 20 is shown a battery of sewage digesters.Numeral 2i may indicate a screening chamber for removal of roughage.

The respective operating connections in the diagrams are shown in theway of arrowed lines, the arrows indicating the flow direction in thelines.

More specifically, Fig. 1 includes an influent line 22 leading into thecontrol chamber I1, di-' rect feed connections 23 and 24 from thecontrol chamber I! to the clarifiers l and II respec; tively,overflow-lines 25 and 26 from the clariflers. The numerals 21 and 28indicate the respective clarifier underflow or sludge lines.

In Fig. 2, an influent line '29 leads into the control chamber 11,continuing into a feed line 30 to the clarifler [0. An overflow line 3|from clarifier I 0 leads into the receiving chamber l6 and the flowcontinues through the mixing chamber l into a feed line 32 leadingtherefrom to the second clarifier II from which leads an overflow line33. Respective clarifier underflow lines 34 and 35are indicated to leadfrom the respective clarifiers l0 and II. Arrows 36 leading from thedispensing arrangement l8 indicate that the line la in this fiowsheet isactive tointroduce a chemical precipitating agent.

In Fig. 3 the influent 31 splits in the mixing chamber l5, to allow thesplit portions to continue individually through the flocculating unitsl3 and I4 as indicated by the respective lines 38 and 39. Correspondingconnections 40 and 4| lead from the flocculating units to the respectiveclariflers Ill and H. Clarifier overflows are shown at 42 and 43. Arrows46 leading from the dispensing arrangement l8 indicate that the line I8ain this fiowsheet is active to introduce a chemical coagulating agentahead of mixer l6 and flocculating devices i2, i3. Clarifier.underflowsare shown at 41 and 48.respectively.

Fig. 4 has an influent 49 passing through the control chamber 11, tocontinue into the feed line -50 toelarifier l0. An overflow line 5|leads from the clarifier ill to the receiving chamber Hand to the mixingchamber l5 where the fiow splits to enter into the two flocculatingsections I3 and 14 respectively, the split portions being indicated at52 and 53. Discharges from both flocculating sections combine in theline 54 to feed the clarifier from which overflow leaves at 55.Underflow from clarifler II is shown at 56 to lead away, while anunderflow or sludge line 51 from clarifler- I enters the digesters I8and 20 respectively in series, digester discharge being indicated at 58.Arrows 50 leading from the dispensing arrange ment I 8 indicate theintroduction of a chemical coagulating agent.

Fig. has influent 60 pass through the control chamber I1, by-passing themixing chamber I5 as by a line 6| to continue into the one flocculatingunit I3 as indicated by the line 62. A feed connection 63 then leadsfrom the flocculating unit 13 to the clarifler I0. An overflow line 60from the clarifler leads back through the receiving chamber I6, tocontinue via the mixing chamber I5 into the second flocculating unit orsection II as indicated by the line 65. A feed connection 66 from thereleads to the second clarifler II from which overflow 61 flows away. Anunderflow line 63 from clarifler I0 leads to the flrst digester ordigestion treatment stage I 5, while a line 63 carries imderflow fromclarifier II to the point of raw feed for recirculation.

Hie enlarged detail of the conditioning and flocculating unit I2 withsuitable pipe connections for selective modes of operation is shownsubstantially in Fig. 6 and Fig. 7. An influent pipe 10 leads through a.gate or valve 1I into the con trol chamber I1, mentioned above. Anothergate, valve or closure means 12 leads from the control chamber I1 intothe receiving chamber I6 which is separated through a'wall 13 from themixing chamber I5 (see Fig. 7). A passage 14 underneath the wall 13leads into the mixing chamber in which is provided a rotary mixingdevice 15 such as a turbo-mixer shown in the further enlarged detailsection of Fig; 8.

The agitator or device may comprise a vertical impeller shaft 150,issupported and rotated'i'rom a drive or motor unit 16 shown to bemounted on beams or channel irons 11, (see Fig. '7). At its lower endthe vertical'shaft 15a carries a rotor or impeller 18, (see Fig. 8)which is shown to consist of a hub 18 carrying a disc 80, which hasextending freely downwardly therefrom radial impeller blades 8|.A'substantially annular stator 82 surrounds the'impeller 18, and whichconsists of a dished annular member 83, having freely extendingtherefrom a set of stator blades 84 to guide the liquid ejected from theimpeller blades. The annular dished member 83 is shown With theseimpellerand guide-blades being open a or exposed as they are, the wallsof the mixing chamber in fact form the housing for this impellerorlow-lift pumping device which otherwise is known of itself. In otherwords, the walls of the mixing chamber or section, which may also becalled a rising channel, section or column, can be said to constitute inconnectionwith the stator, the pressure chamber of the impeller device;or it can be said that the stator 82 is associated with the chamber I5in such a manner as to form a constriction thereof for the pamagetherethrough of the liquid being mixed and lifted. A pipe 81 terminating'undemeath the impeller device serves for the introduction ofconditioning or flocculating agents into the liquid stream to obtainwhat is known as a flash mixing effect when the stream thus dosed isdrawn through the impeller dvice.

In Fig. 6 direct passages or passageways or transitions 88 or 89respectively lead from the mixing chamber I5 over a submerged wallportion 80 into the respective sections I3 and II of a flocculating tank9| defined by the side walls 92 and 33, the influent end 94, theeflluent end 95 having an efliuent launder 96. A removable partition 91divides the launder into two sections 98 and 39. respective ends of thelaunder and have closure valves I02 and I03 respectively; A pair ofsluice gates I04 and I05 control the influent from the mixingchamber I5into the respective flocculating sections I3 and I4.

The control chamber I1 is connected through a passage I06 with anauxiliarychamber I01 from which a connection I08 having valve or closuremeans I09 leads into flocculating section I3, bypassing the receivingchamber I6 and the mixing chamber I5. Through a valve I09a, a connectionor pipe I I0 leads from the auxiliary chamber I01 to the clarifier l0(not shown in Fig. 6), and forms at II I a junction with the efiiuentpipe I00 from the flocculator tank.

A corresponding connection or pipe I I2 from the control chamber I1 isprovided with a valve H3 and leads to a junction II4 with theflocculator effluent pipe IOI and on to the second clarifler II (notshown in Fig. 6). A connection II5 leads from the mixing chamber I5 to apoint of junction II6 with the pipe IIO, a. valve II1 being inserted inthe connection II5. Another corresponding connection II8 leads from themixing chamber I5 to a point of junction HQ with the pipe II2, a valve120 being inserted 'in the connection II8. A pipe I2I having a gate orvalve I22 is shown to lead into the receiving chamber I6, which pipeconstitutes the connection carrying overflow from the clarifler I0 (notshown in Fig. 6).

A horizontal sequence of transverse paddle-like assemblies of paddleshafts I23 carries blades or paddles. I24 for the flocculation units I3and I4,

:to move or rotate about horizontal axes in repetitive paths. The shaftsare shown to be driven by a set of chains I25, I26, I21 andcorresponding sprockets, and a motor or driving unit I28. At I29 and I30respectively, in Fig. 6 there are indicated pipe connections for thereturn or recirculation of clarifier sludge or the like.

Numerals I3I and I32 in Fig. 7 indicate drain connections for theflocculation sections having Operation When operating the system withconnections established according to the diagram of Fig. 1 and forparallel operation of the clarifiers I0 and II, the gates or valves 12and I09, I02 and I03, and H1 and I and I 22' are closed. Raw feed orsewage 22 continually enters the control chamber I1 through gate 1|,where it splits into portions one of which passes through passage I06into the auxiliary chamber I01 and from there through a gate I091: intothe pipe or conduit IIO leading to feed the clarifler tank I0, the otherportion of Eliluent pipes I00 and IOI lead from the 4 through gate I I3to feed through pipe or conduit II2 the other clarifier tank I I. Theflocculating unit is thus completely by-passed. Clarifler overflows 25and 26 respectively may flow to a joint disposal. Clarifler underflowsor sludge discharges may also conjointly lead away. The chemicaldispensing arrangement I8 in this setup is shown to be inactive althoughits use is optional. The operating arrangement established according toFig. 1 may serve at times when no special treatment is needed in the wayof flocculating a dosed or undosed sewage.

The arrangement of Fig. 1 may be modified when it is desired to use achemical coagulant and the mixing device I5, by closing the valves I09aand H3 andopening the valve I2'as well as the valves Ill and I 20, whilemaintaining gates I04 and I05 towards the flocculation zone closed, andstarting the mixer I5 goingwhile adding the chemical through pipe 81from the dispensing device I8 with the clarifier sludge lines 21 and 28leading away.

When operating the system with connections established according todiagram Fig. 2 for series operation of the clarifiers I0 and II, thegates I04- and I05 remain closed to block entrance into the flocculatingdevices I2, I3; valve I I3 is closed and so are valves I2 and Ill.Valves I02 and I03 remain closed. Valve I22 in pipe I2I is now open andactive together with valve I20 in pipe H8. Consequently, raw feed 29 mayenter through open main gate II into the control chamber II, throughpassage I06 into the auxiliary chamber I01, and through open gate I09ainto the conduit I I0 through which it feeds theclarifier I0 which nowbecomes a primary clarifier. Overflow from this clarifier, brieflycalled primary overflow, enters the conduit I2I which brings it throughopen valve I22 into the receiving chamber l6 when a chemical coagulantor precipitation agent may be introduced through pipe 81 prior toentering the mixer I5 in the mixing chamber I5. At this stage the mixereffects a quick vigorous mixing or flash mixing while simultaneouslyinducinga low pressure pumping effect upon the liquid, which pressurecompensates for the drop or head loss incurred in the primary overflow,and which will cause the liquid to enter pipe or conduit II8 with valveI20 open, and through conduit II2 will feed the clarifier II which nowbecomes the secondary clarifier.

The reason for the drop or head loss incurred through transfer fromprimary to secondary clarifier is illustrated in Fig. 9 which makes itclear that while both clarifier overflows are on equal level in the caseof parallel operation, the loss occurs when changing to series operationand the primary overflow drops into the overflow launder of the primary.clarifier I0 from where it must be lifted again to the feed level of thesecondary clarifier I I.

A series operation as described in connection with Fig. 2 is desirablefor instance during certain summer months when it is desired to apply2,187,966 the split up leaving the control chamber I I subsequentflocculation. Therefore, valves I094: and II3, I22, Ill and I20 and I22are closed while flow is permitted to pass through valves 1| and I2,gates I04 and I05, and valves I02 and I03. Consequently, raw feed 31 mayenter into the control chamber II, pass on into the receiving chamberI6, and through the submerged passage l4 via the mixing device I5 intothe mixing chamber I5. The dosing pipe 81 may now be activedischarging acoagulating agent into the flow oi. liquid prior to entering the flashmixing phase of the mixer, such dosing being indicated by the arrows 46in the dosing feed line I8a of Fig. 3. Now the liquid is ready foreflective flocculation of the suspended solids when the flow splits toenter and pass through the' respective fiocculating sections I3 and I4by way of open gates I 04 and I05. The removable partition 9! in theoverflow launder 96 of the flocculating apparatus may now be eiIectiveto receive the individual overflows from the sections I3 and I4 inindividual launder sections 98 and 99 so that the proper proportion ofthe total flow may reach each respective clarifier I0 and II by way ofpipes I00 and IOI through the open valves I 02 and I03 therein.

The clarifier overflows 42 and 43 may conjointly lead away to disposal.The clarifier un-- derflows 41 and 48, both containing chemicallyprecipitated sludge, are in this case shown to be led away to suitabledisposal.

In other words, the operating arrangement of Fig. 3 affords increasedpurity of clarifier overflow irrespective of underflow or sludgetreatment. It is understood that with both clariflers discharging dosedprecipitate the character 01' the sludge thus obtained is not preferablefor the process of. digestion.

The operation according to Fig. 4 answers the demand for a highlypurified clarifier overflow and a clarifier sludge of suchcharacteristics as to be suited for the process of digestion.Consequently, this flowsheet suggests series operation of the clariflersI0 and I I, coagulating and flocculation of the secondary stage, and theuse of undosed primary clarifier underflow or sludge in the digesters I9and 20, as well as digesting undosed primary sludge ,together with dosedsecondary sludge.

Consequently, the operating set up in Fig. 4 is as follows: The valvesH3 and I2, and I09 are closed. Closed are also the valves II! and I20leading from the mixing chamber I5, and the valve I02 in pipe I 00leading from the flocculation apparatus launder 98. Open is the valve I09a from the auxiliary control chamber I01, open the valve I22 in pipe I2| leading into the receiving chamber I6, and open are the gates I04 andI05 into the flocculation tank. Open is the flocculation apparatusdischarge valve I03 leading to the secondary clarifier II. The partition91 is assumed to be removed from the flocculation device launder 95.

Irifluent 49 enters the control chamber I1, and through the auxiliary,chamber III! with the valve I09'a opeuinto the pipe IIO, which carriesthe sewage to the primary clarifier I0 from which settled raw sludgebecomes available for digestion in the digesters I9 and 20 when ledthereto through underflow line 51 (see Fig. 4) Overflow from the primaryclarifier passes through pipe I2 I into the receiving chamber I6, and onthrough the submerged passage I4 via the mixer into the mixing chamber I5. The mixer then of course exercises its additional function ofboosting the pressure head compensating for the drop incurred in theprimary overflow. Again, arrows 59 in the dosing supply line I80indicate that a flocculant enters the liquid through pipe 81 below themixer. The liquid thus conditioned splits to enter through gates I04 andI and flow through the flocculating sections I 3 and I4 of theflocculation tank 9| where the solids in the conditioned liquid undergoa process of flocculation or coalescence in preparation for a moreeffective subsequent sedimentation. Eflluent from both flocculationsections combines in the eflluent launder 96 with the partition 91removed, and throughconduit I 0| and valve I03 reaches the terminalsection of the conduit I I2 and thus to feed the secondary clarifier I Ifrom where overflow 55' and sludge discharge 56 maybe disposed of insuitable-ways as by leading all or a desirable part thereof through theconnection 56a into the digester I9 to be digested therein together withthe primary sludge from the line 51.

The operation according to Fig. 5- involves a further refinement, inthat it aflords. secondary stage dosing for chemical precipitation,independent flocculation. for each clarifler stage, as

well as far-reaching clarifier sludge ultilization pass conduit I08through the first flocculation.

section I3 where solids are flocculated and made settleable by .thepeculiar agitation influence of the flocculating paddles I24. Assumingthe removable partition 91 to be inserted inthe flocculation deviceeiiluent launder 96, the liquid treated in the flocculation section I3may leave through the launder section 98 via the eflluent pipe I00 andvalve I02, in order to feed the primary clarifier I 0 after passingthrough the terminal section of the pipe conduit IIO.

Overflow 64 from the primary clarifier I0 passes by way of pipe l2! andvalve I22 into the receiving chamber IS in preparation for its secondarycoagulation and sedimentation step. That is to say, the liquid afterpassing through the submerged passage I4 may now again be dosed with achemical coagulant through the dosing pipe 81,

with arrows in the dosing feed line I 8a indicating that the line isactive in this respect. The dosed liquid by reason of the boostingefiect of the mixer I5 is drawn into the mixing chamber l5, the boostingpressurebeing suflicient to insure compensation of the head lossincurred in the primary clarifier overflow and to cause the flow ofliquid to pass through open gate I05 and through the second flocculationsection I4 and to reach the secondary clarifler I I by way of effluentpipe I 0| and the terminal section of the pipe 2 (not shown in Fig. 6).Overflow from the secondary clarifier I I may leave through 61 tosuitable disposal. Underflow or sludge from the secondary clarifier mayadvantageously be utilized for recirculation or redistribution withinthe plant as by reintroducing it into the control chamber IT or theauxiliary chamber I01, via the pipes I29 and I30 respectively.

A divisional patent application has been filed by me on December '18,1937, covering subject:-

matter carved from this patent,

I claim:

1. A clarification system iorthe removal of suspended solids fromflowing liquids, and equipped for conditioning of the liquid preparatoryto sedimentation, which system comprises a raw liquid supply, a pair ofclariflers substantially arranged at an elevation for paralleloperation, means for selectively conducting liquid from said raw liquidsupply to said clariflers so that under one set of selected conditionsthe clariflers are arranged in parallel and so that under another set ofselected conditions said clariflers are arranged in series whereby theyfunction-as associated primary and secondary clariflers, said meanscomprising a mixing section arranged to receive liquid obtained fromsaid raw liquid supply and wherein the liquid received therein can besubjected to a conditioning operation, and a mixing device in saidmixing sectiomwhich said device includes impeller means surrounded bythe walls of said mixing section in a manner to substantially form a.housing for the impeller means, said impeller means being effective toboost the hydraulic head of the liquid passing through said mixingsection, said means when arranged for series operation being arranged tohave said mixing chamber interposed between the primary and thesecondary clarifier to efiect eflicient mixing of any added conditioningmaterial and of the primary clarifier overflow at a place ahead of thesecondary clarifier, said mixing device also being effective to supplysuflicient hydraulic head to ensure the transfer of liquid from theprimary to the secondary clarifier.

2. A clarification system according to claim 1, characterized by theincluding of an agitating section for effecting flocculation of thesolids in the conditioned liquid, and by the further fact (a) that saidmeans when selectively set for parallel operation of the clarifiers havecontrols for selectively conducting the liquid from the point of rawliquid supply consecutively through the mixing section and past themixing device and thence through said flocculating section, and

(b) that there are controls whereby the volume of the flocculated liquidis split for subsequent parallel treatment of the component volumes insaid clarifiers.

3. A clarificationsystem according to claim 1, characterized by theaddition of an agitating section to effect flocculation of the solids inthe liquid, and by the fact that with the clariflers operating in seriesthe agitating section is operatively interposed'in the flow connectionleading from the mixing section to the secondary clarifier, and by thefurther fact that operating means are providedfor selectively by-passingsaid agitating section.

4. A'clarification system according to claim 1, characterized by theaddition of an agitating section to effect flocculation of the solids inthe liquid, and by the fact that with the clarifiers operating in seriesthe agitating section is operatively interposed in the flow connectionleading from the mixing section to the secondary clarifier, and by thefurther fact that operating means are provided for selectivelyby-passing said agitating section and said mixing section. I

5. A clarification system according to claim 1, characterized by theaddition of an agitating section for the purpose of flocculating thesolids in the liquid, which section comprises a pair of flocculatingunits adapted for parallel operation, and

also characterized by the fact that connections and controls thereforare provided, selectively operable to include one flocculating unit inthe fiow connection between the raw liquid supply and the primaryclarifier,and to include the second fiocculating unit in the flowconnection between the mixing section and the secondary fiocculatingunit and mixer; a feed connection from the fiocculating unit to eachclarlfier, and individual selectively operable closure means for eachconnection; a by-pass: connection between said liquid supply and eachclarifier, and closure means associated therewith selectively operableto eliminate the fiocculating unit; an overflow return conduit betweenone clarifler and said liquid supply, and selectively operable closuremeans associated with said return conduit; all of said connections andclosure means selectively operable in such coordination as to effectchanges of operation substantially as described.

'7. A liquid clarification plant according to claim 6, with the additionof a by-pass connection and selectively operable closure means therefor,arranged between the raw liquid supply and the fiocculating unit forselectively eliminating the mixer. f

8. A liquid clarification plant according toclaim 6, in which thefiocculating unit comprises a.pair of independently operable units, andwith the addition of individual closure means selectively operablebetween said mixer and the respective fiocculating units.

11. A liquid treatment apparatus, which comprises a mixing sectionadapted to have liquid fiow substantially upward therethrough, a rotarycombined mixing and hydraulic pressure-imparting device therein adaptedto have a submerged pressure discharge and which is effective tomaintain above said device in the conditioning section.

- section.

and in horizontal sequence to the latter a subsequent treatment sectionto receive liquid therefrom, said mixing adapted for substantiallyupward fiow therethrough of said liquid and continued flow by way ofhydraulic communication into said fiocculating section; an impellerdevice including a rotor and a stator element interposed in the path ofthe liquid which must pass upwardly through said mixing section andadapted to effect combined mixing and hydraulic lifting of the liquidpassing through the apparatus, said rotor element comprising asubstantially horizontally-extending rotary disc member and radialblades extending downwardly therefrom, said stator comprising asubstantially horizontally.- extending. annulus and radial blades risingtherefrom; said impeller device adapted to have a submerged pressuredischarge and to be effective to .maintain in said mixing section a zoneof relatively-increased hydraulic head at the delivery side of thedevice as compared with a relatively lower hydraulic head at the inletside thereof.

13. In a liquid treatment apparatus having a liquid supply, and having aliquid mixing section and a subsequent treatment section to receiveliquid therefrom, said section adapted for substantially upward flowtherethrough of said liquid and continued flow by way of hydrauliccommunication into said treatment section; an impeller device interposedin the upward path of the liquid through said mixing section and adaptedto have a submerged pressure discharge and to effect combined mixing andhydraulic lifting of the liquid passing through the unit, said impellerdevice comprising a rotor revolving about a substantially vertical axis,and a stator surrounding the same and which is associated with thesurrounding walls of said rising portion so as to form a constrictionthereof for the passage therethrough of the liquid being mixed andlifted, said impeller device, by its operation, being effective ,tomaintain in said mixing section a zone of relatively-increased hydraulichead at the delivery side of the device as compared with a. relativelylower hydraulic head at the opposite side thereof.

14. In a liquid clarification system, an apparatus combination whichcomprises a liquid distributlng section, a liquid supply therefor, aliquid dosing section, a controlled outlet connection leading from saiddistributing section, a con-,

trolled connection between said distributing section and said dosingsection, a pumping pressure section, a pumping device between saiddosing section and said pressure section and through which there existshydraulic communication between the pumping and the dosing sections, a

controlled outlet connection from said pumping pressure section, and acontrolled separate inlet connection as distinguished from saidcontrolled connection between the distributing section and the dosingsection, leading into said dosing REiWIIl-E s. RANKIN.

